Defrosting apparatus

ABSTRACT

A defrosting apparatus for a refrigerator or the like wherein supply of cooling medium to a coil-fin type evaporator is initiated and stopped by sensing the temperature of the evaporator at three locations, namely near the cooling medium inlet of the coil, near a location where the evaporator has the lowest temperature in case the condensation temperature of the cooling medium becomes high due to a rise of atmospheric temperature or the like, and near the cooling medium outlet of the coil, by means of temperature sensing devices switching at 0* C. An electric control circuit is provided which stops the supply of cooling medium when the temperatures at said three locations have dropped to 0* C and initiates again the supply of cooling medium when the temperatures at said three locations have risen above 0* C, so that the supply of cooling medium is not reopened until frost which was formed on the evaporator first and melts last has been removed. Thus, frost formed on the evaporator is necessarily removed perfectly and automatically even when condensation temperature of cooling medium is elevated.

United States Patent 11 1 1111 Nijo Jan. 21, 1975 [54] DEFROSTING APPARATUS [75] Inventor: Kiyoichi Nijo, Osaka, Japan ABSTRACT [73] Assigneez Naniwa sangyo Co Ltd. Osaka A defrosting apparatus for a refrigerator or the like Japan wherein supply of cooling medium to a coil-fin type evaporator is initiated and stopped by sensing the tem- Fllfldi 19, 1973 perature of the evaporator at three locations, namely [2]] App. NO: 416,750 near the cooling medium inlet of the coil, near a location where the evaporator has the lowest temperature in case the condensation temperature of the cooling Foreign pp fl ty Data medium becomes high due to a rise of atmospheric Dec. 15, 1972 Japan 47-125146 temperature or the like, and near the cooling medium outlet of the coil, by means of temperature sensing de- [52] US. Cl. 62/209, 62/227 vices switching at 0 C. An electric control circuit is [51] Int. Cl. F25b 41/00 provided which stops the supply of cooling medium [58] Field of Search 62/156, 209, 227 when the temperatures at said three locations have dropped to 0 C and initiates again the supply of cool- [56] References Cited ing medium when the temperatures at said three loca- UNTTED STATES PATENTS tions have risen above 0 C, so that the supply of cooling medium is not reopened until frost which was 2 33;? formed on the evaporator first and melts last has been 3:703:086 11/1972 Nijto.....ii:iI:....ii.iiiiiii:i:iiiii 62/209 removed-Thus1froslformed the evaporator is essarily removed perfectly and automatically even FOREIGN PATENTS OR APPLICATIONS when condensation temperature of cooling medium is 21,865 1970 Japan 62/209 l vat d Primary ExaminerMeyer Perlin 5 Claims, 2 Drawing Figures DEFROSTING APPARATUS This invention relates to a defrosting apparatus in a domestic refrigerator or the like having an evaporator, and more particularly to a defrosting apparatus which always avoids excessive accumulation of frost on an evaporator for a domestic refrigerator or the like.

The inventor previously developed a novel temperature sensing device which comprises a pair of electrodes and water between the electrodes, thereby switching at C due to the difference in resistivity between liquid water and ice, as disclosed, for example, in US. Pat. No. 3,514,735. By utilizing such temperature sensing devices, the inventor further developed a novel defrosting apparatus for a domestic refrigerator or the like wherein first and second temperature sensing devices are arranged respectively near the cooling medium inlet and outlet of a cooling coil of an evaporator for a domestic refrigerator or the like. An electric control circuit is provided which stops the supply of cooling medium to the evaporator when water in both of the first and second sensing devices has frozen and does not permit further supply of cooling medium until ice in both of the first and second sensing devices has melted, as disclosed, for example, in said US. Pat. No. 3,514,735 (see FIG. 6 and the corresponding disclosure of said Patent). ln this defrosting apparatus, frost formed on the evaporator is removed by melting during the stopping of the supply of cooling medium to the evaporator and said supply of cooling medium or cool ing operation is reopened first when frost on cooling fins near the inlet of cooling coil, where frost is usually formed first, has been removed. The supply of cooling medium or the cooling operation is continued until frost has been formed on cooling fins near the outlet of cooling coil, where frost is formed last, and then is stopped. By such cyclic cooling and defrosting, temperature in the domestic refrigerator or the like is also maintained at approximately constant value.

The above defrosting apparatus is based on an assumption that the temperature of an evaporator always has its lowest value at the inlet of a cooling coil and, therefore, frost is formed first necessarily at a location near said inlet. It is well known, however, that the condensation temperature of a cooling medium rises when atmospheric temperature is high, such as in summer and, in this case, the cooling medium has its lowest temperature at a somewhat lower reach of the cooling coil rather than at the inlet of said coil, namely immediately after the expansion valve for the cooling medium, so that frost is formed on the evaporator first at such lower reach. The aforestated defrosting apparatus, therefore, exhibits the followingdisadvantages when the condensation temperature of the cooling medium becomes high due to a rise of atmospheric temperature or other reasons.

That is, the cooling operation is reopened when some frost still remains on the evaporator because such reopening of cooling operation is ordered by the first sensing device which takes its 0N state when frost near the cooling medium inlet has been removed, but frost at such lower reach, where frost was formed first, has not yet been removed. Such too earlier reopening of the cooling operation will, of course, cause excessive cooling of the atmosphere within the domestic refrigerator or the like so that reserves in the refrigerator will often be deteriorated due to excessive cooling of the same. Further, frost always remaining on the evaporator at such lower reach prevents heat exchange between the evaporator and the atmosphere in the refrigerator so that cooling efficiency is lowered, requiring more power or energy for cooling. For eliminating such disadvantages, it is considered that said first temperature sensing device is displaced according to atmospheric temperature or condensation temperature of cooling medium but, in practice, that is too inconvenient.

Accordingly, the present invention aims at providing a novel defrosting apparatus which eliminates the aforestated disadvantages of the defrosting apparatus according to the prior art.

The invention and its attendant advantages will become more readily apparent as the specification is considered in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic view of an embodiment of the defrosting apparatus according to the present invention; and

FIG. 2 is an enlarged sectional view of a temperature sensing device employed in thedefrosting apparatus shown in FIG. 1.

Referring now to the drawings, there is shown in FIG. 1 an evaporator 10 for a domestic refrigerator or the like. The evaporator 10 comprises a cooling coil 11 for flowing cooling medium or coolant therethrough and a number of spaced cooling fins 12 which are fixedly attached to the coil. The coil 11 has a coolant inlet 11a and a coolant outlet 11b and, as is usual, between the inlet and the outlet is connected a refrigerating mechanism comprising compressor or refrigerating machine, condenser, expansion valve and the like (not shown). Behind the evaporator 10 is arranged a pair of cooling fans 13 which are always driven to rotate so that the air in the refrigerator is forcedly brought into convection current.

According to the present invention, three temperature sensing devices, namely first, second and third temperature sensing devices 14A, 14B and 14C, are provided in a manner detailed hereinafter. The first device 14A is fixedly attached to a cooling fin 12 near the inlet 11a of the cooling coil 11 so that said device 14A senses the temperature of the evaporator 10 near said inlet 11a. The second device 14B is fixedly attached to a cooling fin 12 near a location on the evaporator 10 where said evaporator has its lowest temperature in case the condensation temperature of the cooling medium reaches the highest value during use of the refrigerator so that said device 148 senses the temperature of the evaporator 10 at such location. Further, the third device 14C is fixedly attached to a cooling fin 12 near the outlet 11b of the cooling coil 11 so that said device 14C senses the temperature of the evaporator 10 near said outlet 11b.

Each of the first, second and third temperature sensing devices 14A, 14B and 14C is constructed in a fashion as shown in FIG. 2. The temperature sensing device 14 shown in FIG. 2 comprises a cylindrically shaped housing 15 of metal, which contains water 16. A plug 17 of non-conductive material seals the upper opening of the housing 15. An electrode 18 extends through the plug 17 into the housing 15 so as to be immersed in the water 16. A terminal 19 is connected to the electrode 18, and the housing 15 is fixedly attached to a cooling fin 12, as in the case of the aforestated devices 14A, 14B and 14C. When an electric potential is applied between the terminal 19 and the housing 15, an electric current flows between said terminal 19 and the housing 15 when the water 16 is in liquid state due to the small resistivity of liquid water. However, a current does not flow substantially when the water 16 becomes solidified into ice at C due to the relatively high resistivity of ice. Therefore, the device 14 acts as a switch operating at 0 C whereby a temperature of 0 C is sensed.

In general, each of the first, second and third temperature sensing devices employed in the defrosting apparatus according to the present invention comprises a pair of electrodes (in the case of the device shown in FIG. 2, the housing and the electrode 18) and water between the electrodes, thereby switching at 0 C due to the difference in resistivity between liquid water and ice. Variations and modifications of such temperature sensing device are disclosed, for example, in said U.S. Pat. No. 3,514,735.

Turning again to a consideration of FIG. 1, an electric control circuit 20 is connected to said first, second and third devices 14A, 14B and 14C. The circuit 20 includes an electric power source 21 which is connected through a transformer 22 to a power output 23 having a terminal 24 connected to the terminals 19A, 19B and 19C of the devices 14A, 14B and 14C and another terminal 25 for supplying electric power to each of transistors detailed later. The housings of the devices 14A, 14B and 14C are commonly grounded at 26 through the coil 11 and the fins 12. Each of the terminals 19A, 19B and 19C of the devices 14A, 14B and 14C is connected to the bases of a pair of series-connected transistors 27A. 28A; 27B, 28B; or 27C, 28C through a condenser 29A, 29B or 29C so that electric current flowing between the emitter and base of each transistor is amplified by electric current flowing between the electrode and housing of each of the temperature sensing devices. Each pair of the transistors is in turn connected to a micro-relay 30A, 30B or 30C so that the micro-relay is energized when electric current flowing between the emitter and base of associated transistors is amplified. The control circuit 20 further includes a relay 31 which is connected to the power source 21 and to the micro-relays 30A, 30B and 30C. The relay 31 in turn includes a switch 32 for actuating the refrigerating machine driving means (not shown) which is connected to terminals 33 and 34. The relay 31 further includes a so-called self-maintenance circuit 35 having a coil 35a and a movable contact 35b, which circuit is connected to the micro-relays so that the circuit 35 opens the switch 32 when all of the three micro-relays 30A, 30B and 30C have been deenergized and closes said switch 32 when all of said three micro-relays have been energized, as shown in FIG. 1.

In the embodiment shown in FIG. 1, a further temperature sensing switch means 36 is provided in the refrigerator for sensing the temperature of atmosphere in said refrigerator. Said means 36 is such that is employed in a usual thermostat and makes a switching operation at a variable set temperature so that it takes an ON state above the set temperature and an OFF state below said temperature. The switch means 36 is connected in series to the third temperature sensing device 14C, as shown in FIG. 1.

The defrosting apparatus shown in FIG. 1 operates as follows: Before the refrigerator is cooled, considerable current flows through each of the first, second and third temperature sensing devices 14A, 14B and 14C so that all of the micro-relays 30A, 30B and 30C are energized by the transistors 27A, 28A; 27B, 28B; and 27C, 28C, whereby the switch 32 is closed to operate the refrigerating machine. Thus, cooling medium is supplied to the evaporator 10 so that the atmosphere in the refrigerator is gradually cooled. In this case, the temperature sensing switch means 36 is, of course, in an ON state.

As cooling proceeds, frost is formed gradually on the evaporator 10. This formation of frost begins at a location on the evaporator where the cooling coil 11 or cooling medium flowing therethrough has the lowest temperature. Therefore, frost is formed on the evaporator 10 first near the first device 14A when the condensation temperature of the cooling medium is relatively low and near the second device 148 when said condensation temperature becomes high due to a rise of atmospheric temperature or other reasons. In any event, water in the first or second detector 14A or 148 near which frost is formed first becomes solidified into ice first so that the micro-relay 30A or 308 associated with the particular device is deenergized. In this case, however, the switch 32 in the relay 31 is not opened due to electric current flowing through the coil 35a of the self-maintenance circuit 35 which current keeps the movable contact 35b in the ON position.

When cooling proceeds further, frost is formed on the evaporator 10 near the second or first device 148 or 14A which still contains liquid water so that water in the said device 14B or 14A becomes solidified, whereby the micro-relay 308 or 30A associated with said device is deenergized. In this case, too, the switch 32 is not opened due to the presence of the selfmaintenance circuit 35. The switch 32 for actuating the refrigerating machine is opened first after a further cooling either when frost has been formed near the outlet llb of the cooling coil 11 and the third device 14C so that water in the third device 14C becomes solidified into ice or when the atmosphere in the refrigerator has been cooled to the set temperature on the switch means 36. In this case, the micro-relay 30C is deenergized so that electric current flowing through the coil 35a is cut off to cause displacement of the movable contact 35b to OFF position whereby the switch 32 is opened. The supply of cooling medium to the evaporator 10 is thus stopped. At this point in time, frost formed on the evaporator near the first and second devices 14A and 14B has been supercooled below 0 C.

During the stopping of the supply of cooling medium to the evaporator 10, frost on said evaporator gradually melts. This melting or removal of frost proceeds gradually from the lower reach of the coil 11 to the upper reach of said coil. Due to stopping of the supply of cooling medium, the third sensing device 14C or the switch means 36 which has taken an OFF state takes an ON state due to thte melting of ice in the device 14C or a rise in the temperature of the atmosphere in the refrigerator to the set temperature on the means 36 so that electric current begins to flow through the third device 14C whereby the micro-relay 30C is energized again. In this case, however, the switch 32 for actuating the refrigerating machine is not closed because the movable contact 35b in the self-maintenance circuit 35 is in the OFF position. As the stopping of the supply of cooling medium to the evaporator 10 continues further, frost on the evaporator near the first and second devices 14A and 14B begins to melt. The melting of frost at such locations occurs first near the first device 14A or 148 which was turned into the OFF state later than the other device 14A or 148, as can easily be understood, and occurs then near the other device 14A or 143 which was turned into an oFF state earlier than said first device. The switch 32 is still not closed, when only one of the first and second devices 14A and 14B turns into the ON state due to melting of frost near said one device and therefore melting of ice in said one device, because energizing of only one of themicro-relays 30A and 30B does not cause displacement of the movable contact 35b to its ON position. The switch 32 for actuating the refrigerating machine is closed only when both of the first and second devices 14A and 148 turn to an ON state so that both of the micro-relays 30A and 30B are energized. Supply of cooling medium to the evaporator is thus initiated again or-reopened only when frost on said evaporatorhas been removed perfectly. Thereafter, the defrosting apparatus shown in FIG. 1 repeats the above operation.

During the stopping of the supply of cooling medium to the evaporator 10, frost, especially supercooled frost near the first and second sensing devices 14A and 14B,

takes heat or calories corresponding to latent heat for melting away from air surrounding the frost as said frost melts so that said air is cooled. Such cooled air is forcedly circulated in the refrigerator by the fans 13 so that the temperature of the atmosphere in the refrigerator is maintained at approximately constant value even when the supply of cooling medium to the evaporator is stopped.

in addition, when humidity in the refrigerator is very low or the water content of reserves in the'refrigerator is low, little frost is formed on the evaporator. Even in this case, the defrosting apparatus shown in FIG. 1 operates in a like manner because the temperature of the evaporator is lowered and raised in a same manner as stated before.

As can be understood from the above, the defrosting apparatus according to the present invention removes frost on an evaporator employed in a refrigerator perfectly and automatically even when the condensation temperature of the cooling medium becomes high due to a rise of atmospheric temperature or other reasons such as, for example, a rise in the temperature of repeatedly used cooling air for a condenser for condensing the cooling medium before the evaporator. Further, as can also be understood now, the defrosting apparatus acts as a temperature control apparatus which always maintains temperature in the refrigerator at an approximately constant value notwithstanding various changes in atmospheric temperature and the amount and character of reserves in the refrigerator.

Needless to say, the defrosting apparatus according to the present invention is much simpler in construction and is offered with much lower cost than a defrosting apparatus of water spray type, heater type, hot gas type or the like according to the prior art. In addition, the third temperature sensing device arranged near the outlet of the cooling coil prevents so-called liquid return to a compressor for the cooling medium because the said device stops the flow of cooling medium when the medium isgoing to leave the evaporator below a temperature of 0 C.

While the invention has been described by means of a specific example and in a specific embodiment. it is not intended to be limited thereto, for obvious modifications will occur to those skilled in the art without dcparting from the spirit and scope of the invention.

What is claimed is:

l. in a domestic refrigerator having an evaporator comprising a cooling coil and coolingfins attached to the cooling coil, a defrosting apparatus comprising a first temperature sensing device mounted in heat transfer relation with a cooling medium inlet of the cooling coil for sensing the temperature of the evaporator near said inlet, a second temperature sensing device mounted in heat transfer relation with the evaporator where said evaporator has its lowest temperature in case the condensation temperature of the cooling medium becomes high due to a rise of atmospheric temperature for sensing the temperature of the evaporator near said location, a third temperature sensing device mounted in heat transfer relation with a cooling medium outlet of the cooling coil for sensing the temperature of the evaporator near said outlet, each of the temperature sensing devices comprising a pair of electrodes and water between the electrodes for switching at 0 C due to the difference in resistivity between liquid water and ice, and an electric control circuit for stopping the supply of cooling medium to the evaporator when water in all of the first, second and third sensing devices has frozen and continues stopping of the supply of cooling medium until ice on allof the first, second and third sensing devices has melted.

2. The defrosting apparatus as claimed in claim l wherein said first, second and third temperature sensing devices are attached to the cooling fins.

3. The defrosting apparatus as claimed in claim 1 including temperature sensing switch means which senses the temperature of atmosphere in the domestic refrigerator and takes an ON state above a required temperature and an OFF state below a required temperature connected in series to said third temperature sensing device.

4. The defrosting apparatus as claimed in claim 1 wherein said electric control circuit controls initiating and stopping of refrigerating machine connected to said evaporator.

5. The defrosting apparatus as claimed in claim 4 wherein said electric control circuit includes amplifying means for electric current flowing between the electrodes of each of the sensing devices, a micro-relay for each sensing device which is energized by electric current flowing between the electrodes of the associated sensing device and through said amplifying means, and a relay including switch means for initiating and stopping the refrigerating machine, the said relay further including a self-maintenance circuit which opens the switch means when all of the three micro-relays have been deenergized and closes the switch means when all of the three micro-relays have been energized again. 

1. In a domestic refrigerator having an evaporator comprising a cooling coil and cooling fins attached to the cooling coil, a defrosting apparatus comprising a first temperature sensing device mounted in heat transfer relation with a cooling medium inlet of the cooling coil for sensing the temperature of the evaporator near said inlet, a second temperature sensing device mounted in heat transfer relation with the evaporator where said evaporator has its lowest temperature in case the condensation temperature of the cooling medium becomes high due to a rise of atmospheric temperature for sensing the temperature of the evaporator near said location, a third temperature sensing device mounted in heat transfer relation with a cooling medium outlet of the cooling coil for sensing the temperature of the evaporator near said outlet, each of the temperature sensing devices comprising a pair of electrodes and water between the electrodes for switching at 0* C due to the difference in resistivity between liquid water and ice, and an electric control circuit for stopping the supply of cooling medium to the evaporator when water in all of the first, second and third sensing devices has frozen and continues stopping of the supply of cooling medium until ice on all of the first, second and third sensing devices has melted.
 2. The defrosting apparatus as claimed in claim 1 wherein said first, second and third temperature sensing devices are attached to the cooling fins.
 3. The defrosting apparatus as claimed in claim 1 including temperature sensing switch means which senses the temperature of atmosphere in the domestic refrigerator and takes an ON state above a required temperature and an OFF state below a required temperature connected in series to said third temperature sensing device.
 4. The defrosting apparatus as claimed in claim 1 wherein said electric control circuit controls initiating and stopping of refrigerating machine connected to said evaporator.
 5. The defrosting apparatus as claimed in claim 4 wherein said electric control circuit includes amplifying means for electric current flowing between the electrodes of each of the sensing devices, a micro-relay for each sensing device which is energized by electric current flowing between the electrodes of the associated sensing device and through said amplifying means, and a relay including switch means for initiating and stopping the refrigerating machine, the said relay further including a self-maintenance circuit which opens the switch means when all of the three micro-relays have been deenergized and closes the switch means when all of the three micro-relays have been energized again. 